The present invention relates to the technical field of combustion engines, and more particularly to the design of cylinder head intake ducts and to the associated sizing machining.
The subjects of the present invention are an intake duct, a cylinder head exhibiting at least one such intake duct, the method of manufacturing it, and an engine equipped with such a cylinder head.
This invention finds a favored, but nonexclusive, application in spark-ignition engines.
In spark-ignition engines, there is a desire to generate within the combustion chambers a structured aerodynamic of the “tumble” type (rotational movement about an axis perpendicular to the inter-intake valves plane).
It is desirable to be able to make the best possible use of this turbulence, particularly at the time of ignition, because it ensures greater combustion speeds, particularly under part load conditions. The turbulence therefore increases the potential for dilution with residual burnt gases in the chamber, and this results directly in a saving on fuel consumption. Furthermore, the “tumble” makes it possible to operate at a great deal less advance under cold start conditions, and thus to recover heat from the exhaust, for catalytic converter light off. Finally, for full load at low speed, the “tumble” also speeds up combustion, making it possible to operate with a great deal less ignition advance, while at the same time repelling pinging.
In general, the aim is to obtain an aerodynamic “tumble” movement of a certain intensity, while at the same time maintaining enough permeability to ensure the level of performance of the engine. The shape of the duct has also to fulfill the functionalities of fuel consumption and pollution reduction, when demands are made on the engine. Finally, it has also to be simple to produce and robust in its manufacture.
The fact of the matter is that the four main functionalities to be optimized in an engine (pollution reduction, response to demand, fuel consumption and pinging) are closely connected with the “tumble” and require a great deal of robustness in the manufacture of the engine. The geometric shapings of the intake duct with a view to achieving an aerodynamic package of the “tumble” type have therefore to be particularly robust with regard to casting spread. Such ducts must not under any circumstance introduce disparities in aerodynamic intensity, or in permeability, as these would be to the detriment of the functionalities of pollution reduction, fuel consumption and performance.
In order not to generate too pronounced a step or a ramp which would cause a drop in permeability, the bottom part of the duct casting is generally produced round, so that it mates well with the ogiva machining tool, which of necessity is round. Now, square ducts encourage “tumble”. The shape of the duct has therefore to incorporate a transition zone, forming the transition between a square section and a round section.
Publication JP2003214169 describes an intake duct of the “tumble” type which, in cross section, has a recess in the duct casting. This recess forms a ramp which guides the airstream toward the front of the valve. A ramp such as this is admittedly favorable to the swirling movement of the intake air, but creates too great a deviation on the airstream not to have any effect on the flow of the air.